In semiconductor processing, physical vapor deposition (PVD) is a conventionally used process for depositing a thin film. A PVD process generally includes bombarding a target comprising a source material with ions from a plasma, causing the source material to be sputtered from the target. The ejected source material is then accelerated towards a substrate being processed via a voltage bias, resulting in a deposition of the source material with or without reaction with other reactant.
In recent years, PVD process has been increasingly used to deposit dielectric materials replacing chemical vapor deposition (CVD). Compared to dielectric films formed by CVD, dielectric films formed by PVD have less contamination, thus, higher quality. Typical pulsed DC PVD vacuum chamber hardware contains a substrate pedestal, a process kit, including process shield (s), and a source, including a target. Usually, the target (cathode) is charged and the process shield is grounded (anode) to sustain plasma. Using the shield as an anode operates well with metal deposition but creates problems with dielectric deposition.
However, depositing dielectric material in a PVD chamber is accompanied by inner surfaces of the PVD chamber slowly coated by a non-conductive dielectric material. Because inner shields of PVD chambers function as system anodes during processing, the dielectric coating on the inner surfaces can cause variation in circuit impedance and voltage distribution. The dielectric coating may also change plasma distribution inside the PVD chamber thus negatively impacts deposition rate and uniformity of film thickness. Ultimately, the dielectric coating may even cause circuit interruption and disappearing anode problems. As a result, a metal pasting process is used on the shield to recover the grounding (anode). The pasting process hinders throughput performance of the chamber.
Thus, there is need for apparatus for maintaining the inner surfaces of a PVD chamber conductive during deposition of dielectric materials.